The capture and detection of ionizing radiation in an efficient way, without significant loss or degradation of the image information, is of paramount significance in medical imaging. Recent advances in medical detector technology make it possible for superior images to be produced by digital electronic techniques, such as digital radiography, as opposed to classical film-screen techniques. In fact, new methods of radiographic imaging that utilize advances in electronics and computer technology have been shown to improve diagnostic quality and allow for new diagnostic modalities with reduced patient dose. Specifically, digital radiography has many advantages over conventional radiography such as expanded display of detector dynamic range, fast image acquisition and display, convenient storage, transmission and display of stored images without degradation, extended capabilities of data analysis and image processing, and reduced patient dose.
Different detector technologies and beam geometries have been proposed for digital radiography, such as scintillator-photodiode systems, high-pressure gas filled detectors, scintillator-photomultiplier systems, kinestatic charge detectors, proximity image intensifier/CCD devices, phosphor screen-photodiode systems and diode arrays.
Some of the disadvantages of known digital radiographic systems are the relatively high initial cost and the limited detector resolution. The efficient detection of X-ray radiation is the main problem in digital radiography, computed tomography, and affiliated disciplines. Recent advances in medical detector technology suggest that superior radiation images may be produced by means of digital electronic techniques. In particular, recent advances in electronics and computer technology have provided improved diagnostic quality and diagnostic modalities while reducing doses of incident radiation. Though several new detectors have been proposed for digital radiography and computed tomography, there is still no single technology of choice that addresses all of the issues for optimal imaging. The technology of choice depends upon several image quality criteria such as high quantum and energy absorption efficiency, high detector quantum efficiency (DQE), high spatial resolution, negligible scattered acceptance, detector geometry, fast readout, high dynamic range, image correction and display capabilities, and of course, acceptable cost. One of the primary problems with digital radiography is the detection of scattered radiation which reduces the contrast of the image. Known line scanning techniques inefficiently utilize the X-ray tube output. This limitation can be overcome by utilizing a wider slot-shaped X-ray beam and collection of multiple lines simultaneously.
One approach to overcome the aforementioned disadvantages is discussed in the patent application U.S. Ser. No. 60/011,499, which is incorporated herein by reference. The approach disclosed therein provides a dual-energy gas microstrip wherein low energy and high energy images are obtained and are compared to provide a high contrast image. Although this approach is effective, it only employs a single medium, the gas surrounding the microstrip, to develop the dual image. Through further research, new devices have been developed which further improve these detection techniques. These devices are described in U.S. patent application Ser. No. 09/078,991 incorporated herein by reference. While this invention provides good spatial and contrast resolution with low dose, the image quality and image contrast could be improved.
In particular, ion and electron interaction within the detector creates random ion/electron motion within the detector element. This motion is detected along with the primary ion/electron flow created by the target. Since the motion is random, it does not completely occlude the image, but reduces the image quality by creating ghost images, cloudiness, or reduced contrast, collectively referred to as noise. Therefore, a need exists for a detector that provides an improved image by reducing the detection of random ion/electron motion. An additional need exists for a detector that amplifies the primary ion/electron flow improving image signal, improving the signal to noise ratio, and generating better contrast between the images.